Electrostatic chuck

ABSTRACT

According to the embodiment, the first invention relates to an electrostatic chuck. The electrostatic chuck includes a ceramic dielectric substrate having a first major surface placing a suction object and a second major surface on an opposite side to the first major surface, a base plate supporting the ceramic dielectric substrate and including a gas introduction path, and a first porous part provided at a position between the base plate and the first major surface and being opposite to the gas introduction path. The first porous part includes sparse portions including pores and a dense portion having a density higher than a density of the sparse portions. Each of the sparse portions extends from the base plate toward the ceramic dielectric substrate. The dense portion is positioned between the sparse portions. The sparse portions include a wall portion provided between the pores and the pores.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-047010, filed on Mar. 14, 2018;Japanese Patent Application No. 2018-203734, filed on Oct. 30, 2018; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electrostatic chuck.

BACKGROUND

An electrostatic chuck made of ceramic manufactured by sandwichingelectrodes between ceramic electrostatic substrates made of alumina andfiring them applies an electrostatic suction power to built-inelectrodes and sucks a substrate such as a silicon wafer or the like byan electrostatic force. In the electrostatic chuck like this, aninactive gas such as helium (He) or the like is flown between a surfaceof the ceramic dielectric substrate and a back side of the substratebeing a suction object, and a temperature of the substrate being thesuction object is controlled.

For example, temperature increase of the substrate may be accompaniedduring processing in a CVD (Chemical Vapor Deposition) apparatus, asputtering apparatus, an ion implantation apparatus, an etchingapparatus or the like in which the substrate is processed. In theelectrostatic chuck used for those apparatus, an inactive gas such as Heor the like is flown between the ceramic dielectric substrate and thesubstrate being the suction object, and the temperature increase of thesubstrate is suppressed by bringing the inactive gas into contact withthe substrate.

In the electrostatic chuck which controls the substrate temperature bythe inactive gas such as He or the like, holes (gas introduction path)for introducing the inactive gas such as He or the like are provided inthe ceramic dielectric substrate and a base plate supporting the ceramicdielectric substrate. Through holes communicating with the gasintroduction path of the base plate are provided in the ceramicdielectric substrate. Thereby, the inactive gas introduced from the gasintroduction path of the base plate is introduced to a back side of thesubstrate through the through holes of the ceramic dielectric substrate.

Here, when processing the substrate in the apparatus, discharge (arcdischarge) from the plasma in the apparatus toward the base plate madeof a metal may be generated. The gas introduction path of the base plateand the through hole of the ceramic dielectric substrate may be likelyto be a path for discharge. Then, there is a technique that resistance(breakdown voltage or the like) to the arc discharge is improved byproviding a porous part in the gas introduction path of the base plateand the through hole of the ceramic dielectric substrate. For example,an electrostatic chuck is disclosed, which insulation property in thegas introduction path is improved by providing a ceramic sintered porousbody in the gas introduction path and making a ceramic sintered porousbody structure and a film pore a gas flow path. An electrostatic chuckis disclosed, which a discharge prevention member made of the ceramicporous body and being a process gas flow path for preventing thedischarge is provided in a gas diffusion gap. An electrostatic chuck isdisclosed, which a dielectric insert is provided as a porous dielectricsuch as alumina and the arc discharge is reduced. It is desired thatwhile securing a resistance to the arc discharge and a flow rate of thegas, a mechanical strength (rigidity) of the porous part is improved inthe electrostatic chuck including the porous part like this.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view illustrating an electrostaticchuck according to an embodiment;

FIG. 2A and FIG. 2B are schematic views illustrating the electrostaticchuck according to the embodiment, FIG. 2C and FIG. 2D are schematiccross sectional views for illustrating a hole part 15 c according toother embodiment;

FIG. 3A and FIG. 3B are schematic views illustrating a first porous partof the electrostatic chuck according to the embodiment;

FIG. 4 is a schematic plan view illustrating the first porous part ofthe electrostatic chuck according to the embodiment;

FIG. 5 is a schematic plan view illustrating the first porous part ofthe electrostatic chuck according to the embodiment;

FIG. 6A and FIG. 6B are schematic plan views illustrating the firstporous part of the electrostatic chuck according to the embodiment;

FIG. 7A and FIG. 7B are schematic views illustrating another firstporous part according to the embodiment;

FIG. 8 is a schematic cross sectional view illustrating theelectrostatic chuck according to the embodiment;

FIG. 9A and FIG. 9B are schematic cross sectional views illustrating theelectrostatic chuck according to the embodiment;

FIG. 10 is a schematic cross sectional view illustrating a second porouspart of the electrostatic chuck according to the embodiment;

FIG. 11 is a schematic cross sectional view illustrating anotherelectrostatic chuck according to the embodiment; and

FIG. 12 is a schematic cross sectional view illustrating anotherelectrostatic chuck according to the embodiment.

DETAILED DESCRIPTION

The first invention relates to an electrostatic chuck. The electrostaticchuck includes a ceramic dielectric substrate having a first majorsurface placing a suction object and a second major surface on anopposite side to the first major surface, a base plate supporting theceramic dielectric substrate and including a gas introduction path, anda first porous part provided at a position between the base plate andthe first major surface of the ceramic dielectric substrate and beingopposite to the gas introduction path. The first porous part includes aplurality of sparse portions including a plurality of holes and a denseportion having a density higher than a density of the sparse portions.Each of the sparse portions extends in a first direction from the baseplate toward the ceramic dielectric substrate. The dense portion ispositioned between the plurality of sparse portions. The sparse portionsinclude a wall portion provided between the holes and the holes, and aminimum value of a dimension of the wall portion is smaller than aminimum value of a dimension of the dense portion in a second directionsubstantially perpendicular to the first direction.

According to the electrostatic chuck, since the sparse portions and thedense portion extending in the first direction are provided in the firstporous part, while securing a resistance to an arc discharge and a gasflow rate, a mechanical strength (rigidity) of the first porous part canbe improved.

The second invention relates to the electrostatic chuck in the firstinvention, wherein a dimension of the plurality of holes provided ineach of the plurality of sparse portions is smaller than the dimensionof the dense portion in the second direction.

According to the electrostatic chuck, since the dimension of theplurality of holes can be sufficiently small, the resistance to the arcdischarge can be further improved.

The third invention related to the electrostatic chuck in the first orsecond inventions, wherein an aspect ratio of the plurality of holesprovided in each of the plurality of sparse portions is not less than30.

According to the electrostatic chuck, the resistance to the arcdischarge can be further improved.

The fourth invention relates to the electrostatic chuck in the one ofthe first to third inventions, wherein a dimension of the plurality ofholes provided in each of the plurality of sparse portions is not lessthan 1 micrometer and not more than 20 micrometers in the seconddirection.

According to the electrostatic chuck, since the holes having thedimension of 1 to 20 micro meters and extending in one direction can bearranged, the high resistance to the arc discharge can be realized.

The fifth invention relates to the electrostatic chuck in one of thefirst to fourth inventions, wherein when viewed along the firstdirection, the first hole is positioned at a center portion of thesparse portions, and a number of holes of the plurality of holesadjacent to the first hole and surrounding the first hole is 6.

According to the electrostatic chuck, in a plan view, it is possible todispose the plurality of holes with high isotropy and high density.Thereby, while securing the resistance to the arc discharge and the flowrate of the flowing gas, the rigidity of the first porous part can beimproved.

The sixth invention relates to the electrostatic chuck in one of thefirst to fifth inventions, further comprising: an electrode providedbetween the first major surface and the second major surface. A distancein a second direction between a porous region provided in the firstporous part and the electrode is longer than a distance in a firstdirection between the first major surface and the electrode.

According to the electrostatic chuck, the discharge in the first porouspart can be suppressed by lengthen the distance in the second directionbetween the porous region provided in the first porous part and theelectrode. The suction force of the object placed on the first majorsurface can be increased by shortening the distance in the firstdirection between the first major surface and the electrode.

The seventh invention relates to the electrostatic chuck in one of thefirst to sixth inventions, further comprising: a second porous partprovided between the first porous part and the gas introduction path. Adimension of the second porous part is larger than a dimension of thefirst porous part in the second direction.

According to the electrostatic chuck, since a higher breakdown voltagecan be obtained by providing the second porous part, the arc dischargecan be suppressed from being generated more effectively.

The eighth invention relates to the electrostatic chuck in one of thefirst to seventh inventions, further comprising: a second porous partprovided between the first porous part and the gas introduction path andincluding a plurality of pores. An average value of diameters of theplurality of pores provided in the second porous part is larger than anaverage value of diameters of the plurality of pores provided in thefirst porous part.

According to the electrostatic chuck, since the second porous parthaving a large pore diameter is provided, the gas flow can befacilitated. Since the first porous part having a small pore diameter isprovided on the suction object side, the arc discharge can be suppressedfrom being generated more effectively.

The ninth invention relates to electrostatic chuck in one of the firstto seventh inventions, further comprising: a second porous part providedbetween the first porous part and the gas introduction path andincluding a plurality of pores. Fluctuation of diameters of theplurality of pores provided in the first porous part is smaller thanfluctuation of diameters of a plurality of pores provided in the secondporous part.

According to the electrostatic chuck, since the fluctuation of thediameters pf the plurality of pores provided in the first porous part issmaller than the fluctuation of the diameters of the plurality of poresprovided in the second porous part, the arc discharge can be suppressedfrom being generated more effectively.

The tenth invention relates to the electrostatic chuck in one of theeighth or ninth invention, wherein a dimension of the second porous partis larger than a dimension of the first porous part in the firstdirection.

According to the electrostatic chuck, since a higher breakdown voltagecan be obtained, the arc discharge can be suppressed from beinggenerated more effectively.

The eleventh invention relates to the electrostatic chuck in one of theeighth to tenth inventions, wherein a plurality of pores provided in thesecond porous part are more dispersed three dimensionally than aplurality of pores provided in the first porous part, and a ratio ofpores piercing in the first direction is larger in the first porous partthan the second porous part.

An example that the pores are dispersed three dimensionally will bedescribed later with reference to FIG. 10.

According to the electrostatic chuck, since the higher breakdown voltagecan be obtained by providing the second porous part including theplurality of pores dispersed three-dimensionally, the arc discharge canbe suppressed from being generated more effectively. The gas flow can befacilitated by providing the first porous part having a large ratio ofpores piercing in the first direction.

Twelfth invention relates to the electrostatic chuck in one of the firstto eleventh inventions, wherein the first porous part and the ceramicdielectric substrate include aluminum oxide as a main component, and apurity of aluminum oxide of the ceramic dielectric substrate is higherthan a purity of aluminum oxide of the first porous part.

According to the electrostatic chuck, performance of the resistance toplasma or the like of the electrostatic chuck can be secured, and themechanical strength of the first porous part can be secured. As oneexample, sintering of the first porous part is assisted by including afine amount of additive to the first porous part, and it is possible tosecure the control of the pore and to secure the mechanical strength.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

In the drawings, the same reference numbers are applied to the sameelements and the detailed description will be omitted as appropriate.

FIG. 1 is a schematic cross sectional view illustrating an electrostaticchuck according to the embodiment.

As shown in FIG. 1, an electrostatic chuck 110 according to theembodiment includes a ceramic dielectric substrate 11, a base plate 50and a first porous part 90.

The ceramic dielectric substrate 11 is, for example, a plate-shaped basematerial of sintered ceramic. For example, the ceramic dielectricsubstrate 11 includes aluminum oxide (Al₂O₃). For example, the ceramicdielectric substrate 11 is formed of a high purity aluminum oxide. Aconcentration of aluminum oxide in the ceramic dielectric substrate 11is, for example, not less than 99 atomic percent (atomic %) and not morethan 100 atomic %. Plasma resistance of the ceramic dielectric substrate11 can be improved by using the high purity aluminum oxide. The ceramicdielectric substrate 11 has a first major surface 11 a having a suctionobject W placed and a second major surface 11 b on an opposite side tothe first major surface 11 a. The suction object W is, for example, asemiconductor substrate such as a silicon wafer or the like.

An electrode 12 is provided on the ceramic dielectric substrate 11. Theelectrode 12 is provided between the first major surface 11 a and thesecond major surface 12 b of the ceramic dielectric substrate 11. Theelectrode 12 is formed to be inserted into the ceramic dielectricsubstrate 11. The electrostatic chuck 110 generates a charge on thefirst major surface 11 a side of the electrode 12 and sucks and holdsthe object W by an electrostatic force produced by application of asuction holding voltage 80 to the electrode 12.

Here, in the description of the embodiment, a direction from the baseplate 50 toward the ceramic dielectric substrate 11 is taken as aZ-direction (corresponding to one example of a first direction), one ofdirections substantially perpendicular to the Z-direction is taken as AY-direction (corresponding to one example of a second direction), and adirection substantially perpendicular to the Z-direction and theY-direction is taken as an X-direction (corresponding to one example ofa second direction).

A shape of the electrode 12 is film-shaped along the first major surface11 a and the second major surface 11 b of the ceramic dielectricsubstrate 11. The electrode 12 is a suction electrode for sucking andholding the object W. The electrode 12 may be either unipolar type orbipolar type. The electrode shown in FIG. 1 is bipolar type, and 2 poleelectrodes 12 are provided on the same plane.

The electrode 12 is provided with a connection part 20 extending to thesecond major surface 11 b side of the ceramic dielectric substrate 11.The connection part 20 is, for example, a via (solid type) and a viahole (hollow type) communicating with the electrode 12. The connectionpart 20 may be a metal terminal connected by an adequate method such asbrazing.

The base plate 50 is a member supporting the ceramic dielectricsubstrate 11. The ceramic dielectric substrate 11 is fixed onto the baseplate 50 by an adhesion part 60 shown in FIG. 2A. The adhesion part 60can be, for example, a hardened silicone adhesive.

The base plate 50 is, for example, made of a metal. The base plater 50is, for example, divided into an upper portion 50 a and a lower portion50 b made of aluminum, and a communicating passage 55 is providedbetween the upper portion 50 a and the lower portion 50 b. One end sideof the communicating passage 55 is connected to an input path 51, andthe other end side of the communicating passage 55 is connected to anoutput path 52.

The base plate 50 also plays a role to adjust a temperature of theelectrostatic chuck 110. For example, when cooling the electrostaticchuck 110, a cooling medium is flown in from the input path 51, ispassed through the communicating passage 55, and is flown out from theoutput path 52. Thereby, a heat of the base plate 50 is absorbed by thecooling medium, and the ceramic dielectric substrate 11 installedthereon can be cooled. On the other hand, when holding the electrostaticchuck 110 warm, it is also possible to put a heat holding medium in thecommunicating passage 55. It is also possible to incorporate a heatingelement in the ceramic dielectric substrate 11 and the base plate 50.The temperature of the object W to be sucked and held by theelectrostatic chuck 110 can be adjusted by adjusting the temperature ofthe base plate 50 and the ceramic dielectric substrate 11.

Dots 13 are provided on the first major surface 11 a side of the ceramicdielectric substrate 11 as necessary, and a groove 14 is providedbetween the dots 13. That is, the first major surface 11 a is an unevensurface and includes a recess and a protrusion. The protrusion of thefirst major surface corresponds to a dot 13 and the recess of the firstmajor surface corresponds to the recess. The groove 14 extendscontinuously in the XY plane. A space is formed between the back side ofthe object W placed on the electrostatic chuck 110 and the first majorsurface 11 a including the groove 14.

The ceramic dielectric substrate 11 includes a through hole 15 connectedto the groove 14. The through hole 15 is provided from the second majorsurface 11 b toward the first major surface 11 a. That is, the throughhole 15 extends from the second major surface 11 b to the first majorsurface 11 a in the Z-direction and pierces the ceramic dielectricsubstrate 11.

The temperature of the object W and the particles adhering to the objectW can be controlled in a favorable state by adequately selecting aheight of the dot 13 (a depth of the groove 14), an area ratio andshapes or the like of the dot 13 and the groove 14.

A gas introduction path 53 is provided in the base plate 50. The gasintroduction path 53 is provided, for example, to pierce the base plate50. The gas introduction path 53 may be provided to reach the ceramicdielectric substrate 11 side by diverging from the middle of the othergas introduction path 53 without piercing the base plate 50. The gasintroduction path 53 may be provided at multiple positions of the baseplate 50.

The gas introduction path 52 is communicated with the through hole 15.That is, the gas (helium (He) or the like) which flows in the gasintroduction path 53 flows in the through hole 15 after passing throughthe gas introduction path 53.

The gas which flows in the gas introduction path 53 flows in the spaceprovided between the object W and the first major surface 11 a includingthe groove 14 after passing through the through hole 15. Thereby, theobject w can be cooled directly by the gas.

The first porous part 90 can be provided, for example, at a positionfacing the gas introduction path 53, the position being between the baseplate 50 and the first major surface 11 a of the ceramic dielectricsubstrate 11 in the Z-direction. For example, the first porous part 90is provided in the through hole 15 of the ceramic dielectric substrate11. For example, the first porous part 90 is inserted into the throughhole 15.

FIG. 2A and FIG. 2B are schematic views illustrating the electrostaticchuck according the embodiment. FIG. 2A illustrates around the firstporous part 90. FIG. 2A corresponds to an enlarged view of a region Ashown in FIG. 1. FIG. 2B is a plan view illustrating the first porouspart 90.

FIG. 2C and FIG. 2D are schematic cross sectional views for illustratinga hole part 15 c according to other embodiment.

In order to be not complicated, dots 13 (for example, see FIG. 1) areomitted in FIG. 2A, FIG. 2C, FIG. 2D.

In this example, the through hole 15 includes a hole part 15 a, and ahole part 15 b (corresponding to one example of a first hole part). Oneend of the hole part 15 a is positioned on the second major surface 11 bof the ceramic dielectric substrate 11.

The ceramic dielectric substrate 11 can include the hole part 15 bpositioned between the first major surface 11 a and the first porouspart 90 in the Z-direction. The hole part 15 b is communicated with thehole part 15 a and extends to the first major surface 11 a of theceramic dielectric substrate 11. That is, one end of the hole part 15 bis positioned on the first major surface 11 a (groove 14). The hole part15 b is a connecting hole connecting the first porous part 90 and thegroove 14. A diameter of the hole part 15 b (a length along theX-direction) is smaller than a diameter of the hole part 15 a (a lengthalong the X-direction). Design freedom of the space formed between theceramic dielectric substrate 11 and the object W (for example, the firstmajor surface 11 a including the groove 14) can be increased byproviding the hole part 15 b with a small diameter. For example, asshown in FIG. 2A, a width of the groove 14 (a length along theX-direction) can be shorter than a width of the first porous part 90 (alength along the X-direction). Thereby, for example, the discharge inthe space formed between the ceramic dielectric substrate 11 and theobject W can be suppressed.

The diameter of the hole part 15 b is, for example, not less than 0.05millimeters (mm) and not more than 0.5 mm. The diameter of the hops part15 a is, for example, not less than 1 mm and not more than 5 mm. Thehole part 15 b may be communicated with the hole part 15 b indirectly.That is, the hole part 15 c (corresponding to one example of a secondhole part) connecting the hole part 15 a and the hole part 15 b may beprovided. As shown in FIG. 2A, the hole part 15 c can be provided in theceramic dielectric substrate 11. As shown in FIG. 2C, the hole part 15 ccan also be provided in the first porous part 90. As shown in FIG. 2D,the hole part 15 c can also be provided in the ceramic dielectricsubstrate 11 and the first porous part 90. That is, at least one of theceramic dielectric substrate 11 and the first porous part 90 can includethe hole part 15 c positioned between the hole part 15 b and the firstporous part 90. In this case, if the hole part 15 c is provided in theceramic dielectric substrate 11, a strength around the hole part 15 ccan be increased, and the generation of chipping or the like around thehole part 15 c can be suppressed. For that reason, the arc discharge canbe suppressed from being generated more effectively. If the hole part 15c is provided in the first porous part 90, the alignment of the holepart 15 c and the first porous part 90 becomes easy. For that reason,the reduction of the arc discharge and the facilitation of the gas flowcan be more easily compatible. Each of the hole part 15 a, the hole part15 b and the hole part 15 c is cylindrical and extends in theZ-direction.

In this case, a dimension of the hole part 15 c can be smaller than adimension of the first porous part 90 and larger than a dimension of thehole part 15 b in the X-direction or the Y-direction. According to theelectrostatic chuck 110 of the embodiment, while securing the flow rateflowing through the hole part 15 b by the first porous part 90 providedat the position facing the gas introduction path 53, the resistance tothe arc discharge can be improved. Since the dimension of the hole part15 c in the X-direction or the Y-direction is made larger than thedimension of the hole part 15 b, most of the gas introduced in the firstporous part 90 with the large dimension can be introduced into the holepart 15 b with the small dimension via the hole part 15 c. That is, thearc discharge can be reduced and the gas flow can be facilitated.

As described previously, the ceramic dielectric substrate 11 includes atleast one groove 14 communicating with the first hole part 15 and opensto the first major surface 11 a. The dimension of the hole part 15 c canbe smaller than the dimension of the groove 14 in the Z-direction. Inthis way, the gas can be supplied to the first major surface 11 a sidevia the groove 14. For that reason, the gas can be easily suppled tobroader area of the first major surface 11 a. Since the dimension of thehole part 15 c in the X-direction or the Y-direction is made larger thanthe dimension of the groove 14 in the X-direction or the Y-direction,the time when the gas passes through the hole 15 c can be short. Thatis, while facilitating the gas flow, the arc discharge can be suppressedfrom being generated more effectively.

As described previously, an adhesion part 60 can be provided between theceramic dielectric substrate 11 and the base plate 50. The dimension ofthe hole part 15 c can be smaller than a dimension of the adhesion part60 in the Z-direction. In this way, the joining strength between theceramic dielectric substrate 11 and the base plate 50 can be improved.Since the dimension of the hole part 15 c in the Z-direction is madesmaller than the dimension of the adhesion part 60, while facilitatingthe gas flow, the arc discharge can be suppressed from being generatedmore effectively.

In this example, the first porous part 90 is provided in the hole part15 a. For this reason, an upper surface 90U of the first porous part 90is not exposed to the first major surface. That is, the upper surface90U of the first porous part 90 is positioned between the first majorsurface 11 a and the second major surface 11 b. On the other hand, alower surface 90L of the first porous part 90 is exposed to the secondmajor surface 11 b.

The first porous part 90 includes a porous region 91 including multiplepores and a dense region 93 denser than the first porous part 90. Thedense region 93 is a region having fewer pores than the porous region 91or a region having substantially no pore. A porosity (percent:%) of thedense region 93 is lower than a porosity (%) of the first porous region91. For that reason, a density (gram/cubic centimeter: g/cm³) of thedense region 93 is higher than the density (g/cm³) of the porous region91. The dense region 93 is dense compared with the porous region 91, andthus for example, the rigidity (mechanical strength) of the dense region93 is higher than the rigidity of the porous region 91.

The porosity of the dense region 93 is, for example, a ratio of a volumeof space (pore) included in the dense region 93 to a total volume of thedense region 93. The porosity of the porous region 91 is, for example, aratio of a volume (pore) included in the porous region 91 to a totalvolume of the porous region 91. For example, the porosity of the porousregion 91 is not less than 5% and not more than 40%, favorably not lessthan 10% and not more than 30%, and the porosity of the dense region 93is not less than 0% and not more than 5%.

The first porous part 90 is columnar (for example, cylindrical). Theporous region 91 is columnar (for example, cylindrical). The denseregion 93 contacts the porous region 91, or is continuous to the porousregion 91. As shown in FIG. 2B, when viewed in the X-direction, thedense region 93 surrounds an outer circumference of the porous region91. The dense region 93 surrounds a side surface 91 s of the porousregion 91 and tubular (for example cylindrical). In other words, theporous region 91 is provided to pierce the dense region 93 in theZ-direction. The gas flown in the through hole 15 from the gasintroduction path 53 passes through multiple pores provided in theporous region 91 and is supplied to the groove 14.

The first porous part 90 including the porous region 91 like this isprovided, and thus while securing the flow rate of the gas flowingthrough the through hole 15, the resistance to the arc discharge can beimproved. The first porous part 90 includes the dense region 93, andthus the rigidity (mechanical strength) of the first porous part 90 canbe improved.

For example, the first porous part 90 is integrated with the ceramicdielectric substrate 11. A state in which two members are integrated isa state in which the two members are chemically bonded by, for example,sintering or the like. A member (for example, adhesive) for fixing onemember to the other member is not provided between the two members. Thatis, other member such as adhesive is not provided between the firstporous part 90 and the ceramic dielectric substrate 11, and the firstporous part 90 and the ceramic dielectric substrate 11 are integrated.

More specifically, in the state in which the first porous part 90 andthe ceramic dielectric substrate 11 are integrated, the side surface(the side surface 93 s of the dense region 93) of the first porous part90 contacts an inner wall 15 w of the through hole 15. The first porouspart 90 is supported by the inner wall 15 w with which the first porouspart 90 is contact, and is fixed to the ceramic dielectric substrate 11.

For example, a through hole is provided in a base material serving asthe ceramic dielectric substrate 11 before sintering, the first porouspart 90 is fitted to the through hole. The ceramic dielectric substrate11 (and the fitted first porous part 90) is sintered in this state, andthus the first porous part 90 and the ceramic dielectric substrate 11can be integrated.

In this way, the first porous part 90 is integrated with the ceramicdielectric substrate 11, and thus fixed to the ceramic dielectricsubstrate 11. Thereby, in comparison with the case of fixing the firstporous part 90 to the ceramic dielectric substrate 11 by the adhesive orthe like, the strength of the electrostatic chuck 110 can be improved.For example, degradation of the electrostatic chuck due corrosion orerosion of the adhesive does not occur.

In the case where the first porous pat 90 and the ceramic dielectricsubstrate 11 are integrated, a force is applied to the side surface ofouter circumference of the first porous part 90 from the ceramicdielectric substrate 11. On the other hand, in the case where multiplepores are provided in the first porous part 90 in order to secure theflow rate of the gas, the mechanical strength of the first porous part90 is reduced. For this reason, there is fear that the first porous part90 is damaged by the force applied from the ceramic dielectric substrate11 to the first porous part 90 when integrating the first porous part 90with the ceramic dielectric substrate 11.

On the contrary, the first porous part 90 includes the dense region 93,and thus the rigidity (mechanical strength) of the first porous part 90can be improved and the first porous part 90 and the ceramic dielectricsubstrate 11 can be integrated.

In the embodiment, the first porous part 90 may not necessarily beintegrated with the ceramic dielectric substrate 11. For example, asshown in FIG. 12, the first porous part 90 may be attached to theceramic dielectric substrate 11 by using the adhesive.

The dense region 93 is positioned between the inner wall 15 w formingthe through hole 15 of the ceramic dielectric substrate 11 and theporous region 91. That is, the porous region 91 is provided inside thefirst porous part 90, and the dense region 93 is provided outside. Thedense region 93 is provided outside the first porous part 90, and thusthe rigidity to the force applied from the ceramic dielectric substrateto the first porous part 90 can be improved. Thereby, the first porouspart 90 and the ceramic dielectric substrate 11 can be easilyintegrated. For example, in the case where an adhesive member 61 (seeFIG. 12) is provided between the first porous part 90 and the ceramicdielectric substrate 11, the gas passing through the first porous part90 can be suppressed by the dense region 93 from contacting the adhesivemember 61. Thereby, the degradation of the adhesive member 61 can besuppressed. The porous region 91 is provided inside the first porouspart 90, and thus the through hole 15 of the ceramic dielectricsubstrate 11 can be suppressed from being closed up by the dense region93 and the flow rate of the gas can be secured.

A thickness of the dense region 93 (a length L0 between the side surface91 s of the porous region 91 and the side surface 93 s of the denseregion 93) is, for example, not less than 100 μm and not more than 1000μm.

An insulative ceramic is used for a material of the first porous part90. The first porous part 90 (each of the porous region 91 and the denseregion 93) includes at least one of aluminum oxide (Al₂O₃), titaniumoxide (TiO₂) or yttrium oxide (Y₂O₃). Thereby, the high breakdownvoltage and the high rigidity of the first porous part 90 can beobtained.

For example, the first porous part 90 includes one of aluminum oxide,titanium oxide and yttrium oxide as a main component.

In this case, a purity of the aluminum oxide of the ceramic dielectricsubstrate 11 can be higher than a purity of the aluminum oxide of thefirst porous part 90. In this way, the performance of the resistance toplasma or the like of the electrostatic chuck 110 can be secured, andthe mechanical strength of the first porous part 90 can be secured. Asone example, sintering of the first porous part 90 is assisted byincluding a fine amount of additive to the first porous part 90, and itis possible to secure the control of the pore and to secure themechanical strength.

In the specification, a ceramic purity such as aluminum oxide of theceramic dielectric substrate 11 can be measured by a fluorescent X-rayanalysis, ICP-AES method (Inductive Coupled Plasma-Atomic EmissionSpectrometry: high-frequency inductively coupled plasma emissionspectrometric analysis method) or the like.

For example, a material of the porous region 91 is the same as amaterial of the dense region 93. However, the material of the porousregion 911 may be different from the material of the dense region 93. Acomposition of the material of the porous region 91 may be differentfrom a composition of the material of the dense region 93.

As shown in FIG. 2A, a distance D1 in the X-direction or the Y-directionbetween the porous region 91 (multiple sparse regions 94 describedlater) and the electrode 12 is longer than a distance D2 in theZ-direction between the first major surface 11 a and the electrode 12.The discharge in the first porous part 90 can be suppressed by lengthenthe distance D1 in the X-direction or the Y-direction between the porousregion 91 provided in the first porous part 90 and the electrode 12. Thesuction force of the object W placed on the first major surface 11 a canbe increased by shortening the distance D2 in the Z-direction betweenthe first major surface 11 a and the electrode 12.

FIG. 3A and FIG. 3B are schematic views illustrating the first porouspart of the electrostatic chuck according to the embodiment.

FIG. 3A is a plan view of the first porous part 90 viewed along theZ-direction, and FIG. 3B is a cross sectional view in a ZY plane of thefirst porous part 90.

As shown in FIG. 3A and FIG. 3B, in this example, the porous region 91includes multiple sparse portions and a dense portion 95. Each of thesparse portions 94 includes multiple pores. The dense portion 95 isdenser than the sparse portions 94. That is, the dense portion 95 is aportion with a fewer pores than the sparse portions 94, or a portionwith substantially no pore. A porosity of the sparse portions 95 islower than a porosity of the dense portion 94. For that reason, thedensity of the dense portion 95 is higher than the density of the sparseportions 94. The porosity of the dense portion 95 may be the same as theporosity of the dense region 93. Since the dense portion 95 is densecompared with the sparse portions 94, the rigidity of the dense portion95 is higher than the rigidity od the sparse portions 94.

The porosity of one sparse portion 94 is, for example, a ratio of thespace (pore) included in the sparse portion 94 to the whole volume ofthe sparse portion 94. The porosity of the dense portion 95 is, forexample, a ratio of the volume of the space (pore) included in the denseportion 95 to the whole volume of the dense portion 95. For example, theporosity of the sparse portion 94 is not less than 20% and not more than60%, favorably not less than 30% and not more than 50%, and the porosityof the dense portion 95 is not less than 0% and not more than 5%.

Each of the multiple sparse portions 94 extends in the Z-direction. Forexample, each of the multiple sparse portions is columnar (cylindricalor polygonal columnar), and is provided to pierce the porous region 91in the Z-direction. The dense portion 95 is positioned between themultiple sparse portions 94. The dense portion 95 is wall-shaped andpartitions the sparse portions 94 which are mutually adjacent. As shownin FIG. 3A, the dense portion 95 is provided to surround the outercircumference of each of the multiple sparse portions 94. The denseportion 95 is continuous to the dense region 93 in the outercircumference of the porous region 91.

The number of the sparse portions 94 provided in the porous region 91 isnot less than 50 and not more than 1000. As shown in FIG. 3A, whenviewed along the Z-direction, the multiple sparse portions 94 havesubstantially the same size. For example, when viewed along theZ-direction, the multiple sparse portions 94 are dispersed isotopicallyand uniformly in the porous region 91. For example, distances betweenthe adjacent sparse portions 94 (namely, a thickness of the denseportion 95) are substantially constant.

For example, when viewed along the Z-direction, a distance L11 betweenthe side surface 93 s of the dense region 93 and the sparse portion 94closest to the side surface 93 s of the multiple sparse portions 94 isnot less than 100 μm and not more than 1000 μm.

In this way, the multiple sparse portions 94 and the dense portion 95which is denser than the sparse portions 94 are provided in the porousregion 91, and thereby, in comparison with the case where multiple poresare dispersed three dimensionally and randomly in the porous region,while securing the resistance to the arc discharge and the flow rate ofthe gas flowing through the through hole 15, the rigidity of the firstporous part 90 can be improved.

For example, if the porosity of the porous region increases, the flowrate of the gas increases, however the resistance to the arc dischargeand the rigidity are decreased. On the contrary, even if the porosity islarge, the resistance to the arc discharge and the rigidity can besuppressed from decreasing by providing the dense portion 95.

For example, when viewed along the Z-direction, a minimum circle, anellipse or a polygon including all of the multiple sparse portions 94are supposed. It can be conceived that the inside of the circle, ellipseor polygon is the porous region 91 and the outside of the circle,ellipse or polygon is the dense region 93.

As described above, the first porous part 90 can include the multiplesparse portions 94 including multiple pores 96 including a first poreand a second pore, and the dense portion 95 having a density higher thea density of the sparse portions 94. Each of the multiple sparseportions 94 extends in the Z-direction. The dense portion 95 ispositioned between the multiple sparse portions 94. The sparse portions94 includes a wall portion 97 provided between the pore 96 (first pore)and the pore 96 (second pore). The minimum value of a dimension of thewall portion 97 can be smaller than the minimum value of a dimension ofthe dense portion 95 in the X-direction or the Y-direction. In this way,since the sparse portions 94 and the dense portion 95 which extend inthe Z-direction are provided in the first porous part 90, while securingthe resistance to the arc discharge and the gas flow rate, themechanical strength (rigidity) of the first porous part 90 can beimproved.

A dimension of the multiple pores 96 provided in each of the multiplesparse portions 94 can be smaller than the dimension of the denseportion 95 in the X-direction or the Y-direction. In this way, since thedimension of the multiple pores 96 can be sufficiently small, theresistance to the arc discharge can be further improved.

A ratio of vertical/side (aspect ratio) of the multiple pores 96provided in each of the multiple sparse portions 94 can be not less than30 and not more than 10000. In this way, the resistance to the arcdischarge can be further improved. More favorably, a lower limit of theratio of vertical/side (aspect ratio) of the multiple pores 96 is notless than 100 and an upper limit is not more than 1600.

In the X-direction or the Y-direction, the dimension of the multiplepores 96 provided in each of the multiple sparse portions 94 can be notless than 1 micro meter and not less than 20 micro meters. In this way,since the pores 96 having the dimension of 1 to 20 micro meters andextending in one direction can be arranged, the high resistance to thearc discharge can be realized.

As shown in FIG. 6A and FIG. 6B described later, when viewed along theZ-direction, the first pore 96 a is positioned at a center portion ofthe sparse portion 94, and the number of pores 96 b to 96 g adjacent tothe first pore 96 a and surrounding the first pore 96 a of the multipleholes 96 can be 6. In this way, when viewed along the Z-direction, it ispossible to dispose the multiple pores 96 with high isotropy and highdensity. Thereby, while securing the resistance to the arc discharge andthe flow rate of the flowing gas, the rigidity of the first porous part90 can be improved.

FIG. 4 is a schematic plan view illustrating the first porous part ofthe electrostatic chuck according to the embodiment.

FIG. 4 shows a portion of the first porous part 90 as viewed along theZ-direction, and corresponds to an enlarged view of FIG. 3A.

When viewed along the Z-direction, each of the multiple sparse portions94 is substantially hexagon (substantially regular hexagon). When viewedalong the Z-direction, the multiple sparse portions 94 includes a firstsparse portion 94 a positioned at the center of the porous region 91 andsix sparse portions 94 (second to seventh sparse portions 94 b to 94 g)surrounding the first sparse portion 94 a.

The second to seventh sparse portions 94 b to 94 g are adjacent to thefirst sparse portion 94 a. The second to seventh sparse portions 94 b to94 g are the sparse portions 94 closest to the first sparse portion 94 aof the multiple sparse portions 94.

The second sparse portion 94 b and the third sparse portion 94 c arearranged with the first sparse portion 94 a in the X-direction. That is,the first sparse portion 94 a is positioned between the second sparseportion 94 b and the third sparse portion 94 c.

A length L1 (a diameter of the first sparse portion 94 a) along theX-direction of the first sparse portion 94 a is longer than a length L2along the X-direction between the first sparse portion 94 a and thesecond sparse portion 94 b, and is longer than a length L3 along theX-direction between the first sparse portion 94 a and the third sparseportion 94 c.

Each of the length L2 and the length L3 corresponds to the thickness ofthe dense portion 95. That is, the length L2 is a length along theX-direction of the dense portion 95 between the first sparse portion 94a and the second sparse portion 94 b. The length L3 is a length alongthe X-direction of the dense portion 95 between the first sparse portion94 a and the third sparse portion 94 c. The length L2 and the length L3are substantially the same. For example, the length L2 is not less than0.5 times and not more than 2.0 times of the length L3.

The length L1 is substantially the same as a length L4 (a diameter ofthe second sparse portion 94 b) along the X-direction of the secondsparse portion 94 b, and substantially the same as a length L5 (adiameter of the third sparse portion 94 c) along the X-direction of thethird sparse portion 94 c. For example, each of the length L4 and thelength L5 is not less than 0.5 times and not more than 2.0 times of thelength L1.

In this way, the first sparse portion 94 a is adjacent to six parseportions 94 of the multiple sparse portions 94 and is surrounded. Thatis, when viewed along the Z-direction, the number of the sparse portions94 adjacent to one sparse portion 94 at the center of the porous region91 is 6. Thereby, in a plan view, it is possible to dispose the multiplesparse portions 94 with high isotropy and high density. Thereby, whilesecuring the resistance to the arc discharge and the flow rate of thegas flowing through the through hole 15, the rigidity of the firstporous part 90 can be improved. Variation of the rigidity to the arcdischarge, variation of the flow rate of the gas flowing through thethrough hole 15, and variation of the rigidity of the first porous part90 can be suppressed.

The diameter of the sparse portions 94 (the length L1, L4, or length L5or the like) is, for example, not less than 50 μm and not more than 500μm. The thickness (the length L2 or L3 or the like) of the dense portion95 is, for example, not less than 10 μm and not more than 100 μm. Thediameter of the sparse portions 94 is larger than the thickness of thedense portion 95. The thickness of the dense portion 95 is thinner thanthe thickness of the dense region 93.

FIG. 5 is a schematic plan view illustrating the first porous part ofthe electrostatic chuck according to the embodiment.

FIG. 5 shows a portion of the first porous part 90 as viewed along thez-direction. FIG. 5 is an enlarged view around one sparse portion 94.

As shown in FIG. 5, in this example, the sparse portions 94 include themultiple pores 96 and the wall portion 97 provided between the multiplepores 96.

Each of the multiple pores 96 extends in the Z-direction. Each of themultiple pores 96 is capillary-shaped (one-dimensional capillarystructure), and pierces the sparse portions 94 in the Z-direction. Thewall portion 97 is wall-shaped and partitions the pores 96 which aremutually adjacent. As shown in FIG. 5, when viewed along theZ-direction, the wall portion 97 is provided to surround the outercircumference of each of the multiple pores 96. The wall portion 97 iscontinuous to the dense portion 95 in the outer circumference of thesparse portion 94.

The number of the pores 96 provided in one sparse portion 94 is not lessthan 50 and not more than 1000. As shown in FIG. 5, when viewed alongthe Z-direction, the multiple pores 96 have substantially the same size.For example, when viewed along the Z-direction, the multiple pores 96are dispersed isotopically and uniformly in the sparse portion 94. Forexample, distances between the adjacent pores 96 (namely, a thickness ofthe wall portion 97) are substantially constant.

In this way, since the pores 96 extending in one direction are arrangedin the sparse portion 94, in comparison with the case where multiplepores are dispersed three dimensionally and randomly in the sparseportions, the high rigidity to the arc discharge can be realized withsmall variation.

Here, “capillary structure” of the multiple pores 96 will be furtherdescribed.

Recently, reduction of circuit line width and miniaturization of circuitpitch for high integration of semiconductors have been furtherproceeding. A further high power is applied to the electrostatic chuck,and the temperature control of the suction object is required at ahigher level. From this background, it is required that whilesuppressing the arc discharge certainly even under a high powerenvironment, the gas flow rate is secured sufficiently and the flow rateis controlled with high accuracy. In the electrostatic chuck 110according to the embodiment, a ceramic plug (the first porous part 90)has been provided for prevention of the arc discharge in the heliumsupply hole (the gas introduction path 53), and then the pore diameter(the diameter of the pore 96) is made small to, for example, a level ofa few to a few tens of μm (the detail of the diameter of the pore 96will be described later). If the diameter becomes small to this level,control of gas flow rate may be difficult. Then, in the invention, forexample, the shape of the pore 96 is further devised to be along theZ-direction. Specifically, the flow rate has been secured by arelatively large pore, and its shape is made complex threedimensionally, and thus the prevention of the arc discharge has beenachieved. On the other hand, in the invention, the prevention of the arcdischarge is achieved by reduction of the diameter of the pore 96 to,for example, a level of a few to a few tens of μm, and the flow rate issecured by simplifying the shape on the contrary. That is, the inventionhas been made on the basis of the idea completely different from theconventional idea.

The shape of the sparse portions 94 is not limited to a hexagon, but maybe a circle (or ellipse) and other polygon. For example, when viewedalong the Z-direction, a minimum circle, an ellipse or a polygonincluding all of the multiple pores 96 arranged with an interval notmore than 10 μm are supposed. It can be conceived that the inside of thecircle, ellipse or polygon is the sparse portions 94 and the outside ofthe circle, ellipse or polygon is the dense portion 95.

FIG. 6A and FIG. 6B are schematic plan views illustrating the firstporous part of the electrostatic chuck according to the embodiment.

FIG. 6A and FIG. 6B show a portion of the fits porous part 90 as viewedalong the Z-direction, and are enlarged views showing the pores 96 inone sparse portion.

As shown in FIG. 6A, when viewed along the Z-direction, the multiplepores 96 include the first pore 96 a positioned at the center portion ofthe sparse portion of the sparse portion 94, six pores 96 (the second toseventh pores 96 b to 96 g) surrounding the first pore 96 a. The secondto seventh pores 96 b to 96 g are adjacent to the first pore 96 a. Thesecond to seventh pores 96 b to 96 g are the pore 96 closest to thefirst pore 96 a of the multiple pores 96.

The second pore 96 b and the third pore 96 c are arranged with the firstpore 96 a in the X-direction. That is, the first pore 96 a is positionedbetween the second pore 96 b and the third pore 96 c.

For example, a length L6 (a diameter of the first pore 96 a) along theX-direction of the first pore 96 a is longer than a length L7 along theX-direction between the first pore 96 a and the second pore 96 b, and islonger than a length L8 along the X-direction between the first pore 96a and the third pore 96 c.

Each of the length L7 and the length L8 corresponds to the thickness ofthe wall portion 97. That is, the length L7 is a length along theX-direction of the wall portion 97 between the first pore 96 a and thesecond pore 97 b. The length L8 is a length along the X-direction of thewall portion 97 between the first pore 96 a and the third pore 96 c. Thelength L7 and the length L8 are substantially the same. For example, thelength L7 is not less than 0.5 times and not more than 2.0 times of thelength L8.

The length L6 is substantially the same as a length L9 (a diameter ofthe second pore 96 b) along the X-direction of the second pore 96 b, andsubstantially the same as a length L10 (a diameter of the third pore 97c) along the X-direction of the third pore 96 c. For example, each ofthe length L9 and the length L10 is not less than 0.5 times and not morethan 2.0 times of the length L6.

For example, if the diameter of the pore is small, the resistance to thearc discharge and the rigidity are improved. On the other hand, if thediameter of the pore is large, the gas flow rate can be large. Thediameter of the pore 96 (the length L6, L9, or L10 or the like) is, forexample, not less than 1 micro meter (μm) and not more than 20 μm. Sincethe pores having the diameter of 1 to 20 μm and extending in onedirection can be arranged, the high resistance to the arc discharge canbe realized with a small variation. The diameter of the pore 96 is morefavorably not less than 3 μm and not more than 10 μm.

Here, a measuring method of the diameter of the pores 96 will bedescribed. An image is obtained with magnification of not less than 1000times by using a scanning electron microscopy (for example, Hitachi HighTechnologies, S-3000). Equivalent circular diameters of 100 pieces forthe pores 96 are calculated by using a commercially available imageanalysis software, and the average value is taken as the diameter of thepores 96.

It is further favorable to suppress the variation of the diameters ofthe multiple pores 96. It is possible to control precisely the flow rateof the flowing gas and the breakdown voltage by making the variation ofthe diameters small. A cumulative distribution of 100 pieces equivalentcircular diameters obtained in the calculation of the above diameters ofthe pores 96 can be used as the variation of the diameters of themultiple pores 96. Specifically, the concept of the particle diameterD50 (median diameter) at 50 vol % of the cumulative distribution and theparticle diameter D90 at 90 vol % used generally for the particle sizedistribution measurement is applied, and the cumulative distributiongraph of the pores 96 taking the horizontal axis as a pore diameter (μm)and taking the vertical axis as a relative pore volume (%) is used, andthen the pore diameter (corresponding to D50 diameter) at 50 vol % ofthe cumulative distribution and the pore diameter (corresponding to D90diameter) at 90 vol % of the cumulative distribution are found. It isfavorable that the variation of the diameters of the multiple pores 96is suppressed to a level satisfying the relationship of D50:D90≤1:2.

The thickness of the wall portion 97 (the length L7, L8 or the like) is,for example, not less than 1 μm and not more than 10 μm. The thicknessof the wall portion 97 is thinner than the thickness of the denseportion 95.

In this way, the first pore 96 a is adjacent to six pores 96 of themultiple pores 96 and surrounded. That is, when viewed along theZ-direction, the number of the pores 96 adjacent to one pore 96 at thecenter portion of the sparse portion 94 is 6. Thereby, in a plan view,it is possible to dispose the multiple pores 96 with high isotropy andhigh density. Thereby, while securing the resistance to the arcdischarge and the flow rate of the gas flowing through the through hole15, the rigidity of the first porous part 90 can be improved. Thevariation of the resistance of the arc discharge, the variation of theflow rate of the gas flowing through the through hole 15, and thevariation of the rigidity of the first porous part 90 can be suppressed.

FIG. 6B shows another example of disposition of the multiple pores 96 inthe sparse portion 94. As shown in FIG. 6B, in this example, themultiple pores 96 are concentrically disposed around the center of thefirst pore 96 a. Thereby, in a plan view, it is possible to dispose themultiple pores with high isotropy and high density.

The first porous part 90 with the structure as described above can bemanufactured, for example, by using extrusion molding. Each of thelengths L0 to L10 can be measured by the observation using a microscopysuch as a scanning electron microscopy.

Evaluation of the porosity in the specification will be described. Here,the evaluation of the porosity of the first porous part 90 will bedescribed as an example.

The image as shown in FIG. 3A is obtained, and a ratio R1 of themultiple sparse portions 94 to the porous region 91 is calculated by animage analysis. A scanning electron microscopy (for example, HitachiHigh Technologies, S-3000) is used for obtaining the image. A BSE imageis obtained at an acceleration voltage of 15 kV and with a magnificationof 30 times. For example, an image size is 1280×960 pixels, and an imagegradation is 256 gradations.

An image analysis software (for example, Win-ROOF Ver6.5 (MitsuyaShouji)) is used for calculation of the ratio R1 of the multiple sparseportions 94 to the porous region 91.

The calculation of the ratio R1 based on Win-ROOF Ver6.5 can be made asfollows.

An evaluation area ROI1 (see FIG. 3A) is assumed to be the minimumcircle (or ellipse) including all sparse portions 94.

Binarization processing by a single threshold (for example, 0) isperformed and an area S1 of the evaluation area ROI1 is calculated.

Binarization processing by two thresholds (for example, 0 and 36) isperformed and a total area S2 of the multiple sparse portions 94 in theevaluation are ROI1 is calculated. At this time, fill-in process in thesparse portions 94 and deletion of regions with a small area which isconsidered to be noise (threshold: not more than 0.002) are performed.The two thresholds are appropriately adjusted by brightness and contrastof the image.

The ratio R1 is calculated as a ratio of the area S2 to the area S1.That is, the ratio R1 (%)=(area S2)/(area S1)×100.

In the embodiment, the ratio R1 of the multiple sparse portions 94 tothe porous region 91 is, for example, not less than 40% and not morethan 70%, favorably not less than 50% and not more than 70%. The ratioR1 is, for example, about 60%.

The image as shown in a plan view of FIG. 5 is obtained, and a ratio R2of the multiple pores 96 to the sparse portion 94 is calculated by theimage analysis. The ratio R2 corresponds to, for example, the porosityof the sparse portion 94. A scanning electron microscopy (for example,Hitachi High Technologies, S-3000) is used for obtaining the image. ABSE image is obtained at an acceleration voltage of 15 kV and with amagnification of 600 times. For example, an image size is 1280×960pixels, and an image gradation is 256 gradations.

An image analysis software (for example, Win-ROOF Ver6.5 (MitsuyaShouji)) is used for calculation of the ratio R2 of the multiple pores96 to the sparse portion 94.

The calculation of the ratio R2 based on Win-ROOF Ver6.5 can be made asfollows.

An evaluation area R012 (see FIG. 5) is assumed to be a hexagon toapproximate the shape of the sparse portion 94. All pores 96 provided inthe sparse portion 94 are included in the evaluation area R012.

Binarization processing by a single threshold (for example, 0) isperformed and an area S3 of the evaluation area R012 is calculated.

Binarization processing by two thresholds (for example, 0 and 36) isperformed and a total area S4 of the multiple pores 96 in the evaluationare R012 is calculated. At this time, fill-in process in the pores 96and deletion of regions with a small area which is considered to benoise (threshold: not more than 1) are performed. The two thresholds areappropriately adjusted by brightness and contrast of the image.

The ratio R2 is calculated as a ratio of the area S4 to the area S3.That is, the ratio R2 (%)=(area S4)/(area S3)×100.

In the embodiment, the ratio R2 of the multiple pores 96 to the sparseportion 94 (the porosity of the sparse portion 94) is, for example, notless than 20% and not more than 60%, favorably not less than 30% and notmore than 50%. The ratio R2 is, for example, about 40%.

The porosity of the porous region 91 corresponds to, for example, aproduct of the ratio R1 of the multiple sparse portions 94 to the porousregion 91 and the ratio R2 of the multiple pores 96 to the sparseportion 94. For example, when the ratio R1 is 60% and the ratio R2 is40%, the porosity of the porous region 91 can be calculated to be about24%.

The first porous part 90 including the porous region 91 having thisporosity is used, and thus while securing the flow rate of the gasflowing through the through hole 15, the breakdown voltage can beimproved.

Similarly, porosities of the ceramic dielectric substrate 11 and asecond porous part 70 can be calculated. The magnification of theelectron scanning microscopy is favorable to be appropriately selectedin a range, for example, a few ten times to a few thousand timesdepending on the observation object.

FIG. 7A and FIG. 7B are schematic views illustrating another firstporous part according to the embodiment.

FIG. 7A is a plan view of the first porous part 90 as viewed along theZ-direction, and FIG. 7B corresponds to an enlarged view of a portion ofFIG. 7A.

As shown in FIG. 7A and FIG. 7B, in this example, a planar shape of thesparse portions 94 is circular. In this way, the planar shape of thesparse portions 94 may not be hexagonal.

FIG. 8 is a schematic cross sectional view illustrating theelectrostatic chuck according to the embodiment.

FIG. 8 corresponds to an enlarged view of the region B shown in FIG. 2.That is, FIG. 8 shows near an interface F1 between the first porous part90 (the dense region 93) and the ceramic dielectric substrate 11. Inthis example, aluminum oxide is used for materials of the first porouspart 90 and the ceramic dielectric substrate 11.

As shown in FIG. 8, the first porous part 90 includes a first region 90p positioned on the ceramic dielectric substrate 11 side in theX-direction or the Y-direction and a second region 90 q continuous tothe first region 90 p in the X-direction or the Y-direction. The firstregion 90 p and the second region 90 q are portions of the dense region93 of the first porous part 90.

The first region 90 p is positioned between the second region 90 q andthe ceramic dielectric substrate 11 in the X-direction or theY-direction. The first region 90 p is a region of about 40 to 60 μm fromthe interface F1 in the X-direction or the Y-direction. That is, a widthW1 (a length of the first region 90 p in a direction perpendicular tothe interface F1) along the X-direction or the Y-direction of the firstregion 90 p is, for example, not less than 40 μm and not more than 60μm.

The ceramic dielectric substrate 11 includes a first substrate region 11p positioned on the first porous part 90 (the first region 90 p) side inthe X-direction or the Y-direction and a second substrate region 11 qcontinuous to the first substrate region 11 p in the X-direction or theY-direction. The first region 90 p and the first substrate region 11 pare provided to contact. The first substrate region 11 p is positionedbetween the second substrate region 11 q and the first porous part 90 inthe X-direction or the Y-direction. The first substrate region 11 p is aregion of about 40 to 60 μm from the interface F1 in the X-direction orthe Y-direction. That is, a width W2 (a length of the first substrateregion 11 p along the direction perpendicular to the interface F1) is,for example, not less than 40 μm and not more than 60 μm.

FIG. 9A and FIG. 9B are schematic cross sectional view illustrating theelectrostatic chuck according to the embodiment.

FIG. 9A is an enlarged view a portion of the first region 90 p shown inFIG. 8. FIG. 9B is an enlarged view of a portion of the first substrateregion 11 p shown in FIG. 8.

As shown in FIG. 9A, the first region 90 p includes multiple particlesg1 (crystal grain). As shown in FIG. 9B, the first substrate region 11 pincludes multiple particles g2 (crystal grain).

An average particle diameter (an average value of diameters of themultiple particles g1) is different from an average particle diameter(an average value of diameters of the multiple particles g2) in thefirst substrate region 11 p.

Since the average particle diameter in the first region 90 p and theaverage particle diameter in the first substrate region 11 p aredifferent, a bonding strength (interface strength) between the crystalgrain of the first porous part 90 and the crystal grain of the ceramicdielectric substrate 11 can be improved at the interface F1. Forexample, separation of the first porous part 90 from the ceramicdielectric substrate 11 and shedding of the crystal grain can besuppressed.

An average value of an equivalent circular diameter of the crystal grainin the cross sectional image such as FIG. 9A and FIG. 9B can be used forthe average particle diameter. The equivalent circular diameter is adiameter of a circle having the same area as the area of the planarshape of the object.

The ceramic dielectric substrate 11 and the first porous part 90 arealso favorably integrated. The first porous part 90 is integrated withthe ceramic dielectric substrate 11, and thus fixed to the ceramicdielectric substrate 11. Thereby, in comparison with the case of fixingthe first porous part 90 to the ceramic dielectric substrate 11 by theadhesive or the like, the strength of the electrostatic chuck 110 can beimproved. For example, degradation of the electrostatic chuck duecorrosion or erosion of the adhesive does not occur.

In this example, the average particle diameter in the first substrateregion 11 p is smaller than the average particle diameter in the firstregion 90 p. Since the particle diameter in the first substrate region11 p is small, the bonding strength between the first porous part 90 andthe ceramic dielectric substrate 11 can be improved at the interfacebetween the first porous part 90 and the ceramic dielectric substrate11. Since the particle diameter in the first substrate region 11 p issmall, the strength of the ceramic dielectric substrate 11 can beimproved and risk of crack or the like due to a stress generated inmanufacturing and processing can be suppressed. For example, the averageparticle diameter in the first region 90 p is not less than 3 μm and notmore than 5 μm. For example, the average particle diameter in the firstsubstrate region 11 p is not less than 0.5 μm and not more than 2 μm.The average particle diameter in the first substrate region 11 p is notless than 1.1 times and not more than 5 times of the average particlediameter in the first region 90 p.

For example, the average particle diameter in the first substrate region11 p is smaller than the average particle diameter in the secondsubstrate region 11 q. In the first substrate region 11 p provided tocontact the first region 90 p, it is favorable to increase the interfacestrength to the first region 90 p due to interaction such as diffusionor the like to the first region 90 p at sintering in a manufacturingprocess, for example. On the other hand, in the second substrate region11 q, it is favorable that original characteristics of the material ofthe ceramic dielectric substrate 11 are developed. The average particlediameter in the first substrate region 11 p is made smaller than theaverage particle diameter in the second substrate region 11 q, and thusthe guarantee of the interface strength in the first substrate region 11p and the characteristics of the ceramic dielectric substrate 11 in thesecond substrate region 11 q can be compatible.

The average particle diameter in the first region 90 p may be smallerthan the average particle diameter in the first substrate region 11 p.Thereby, at the interface between the first porous part 90 and theceramic dielectric substrate 11, the bonding strength between the firstporous part 90 and the ceramic dielectric substrate 11 can be improved.Since the average particle diameter in the first region 90 p is small,the strength of the first porous part 90 increases, and thus thedetachment of the particle in the processing can be suppressed and theparticles can be reduced.

For example, in each of the first porous part 90 and the ceramicdielectric substrate 11, the average particle diameter can be adjustedby adjusting a sintering condition such as a material composition and atemperature. For example, the amount and concentration of the sinteringaid added in the sintering of ceramic materials are adjusted. Forexample, magnesium oxide (MgO) used as the sintering aid suppressesabnormal growth of the crystal grain.

In the same way as described above, the average particle diameter in thefirst region 90 p can also be smaller than the average particle diameterin the second substrate region 11 q. In this way, the mechanicalstrength in the first region 90 p can be improved.

Referring back to FIG. 2A, the description of the structure of theelectrostatic chuck 110 is continued. The electrostatic chuck 110 mayfurther include the second porous part 70. The second porous part 70 canbe provided between the first porous part 90 and the gas introductionpath 53 in the Z-direction. For example, the second porous part 70 isfitted to the ceramic dielectric substrate 11 side of the base plate 60.As shown in FIG. 2A, for example, a counter sunk portion 53 a isprovided on the ceramic dielectric substrate 11 side of the base plate50. The counter sunk portion 53 a is provided to be tubular. The secondporous part 70 is fitted to the counter sunk portion 53 a by adequatelydesigning an inner diameter of the counter sunk portion 53 a.

An upper surface 70U of the second porous part 70 is exposed to an uppersurface 50U of the base plate 50. The upper surface 70U of the secondporous part 70 is opposed to the lower surface 90L of the first porouspart 90. In this example, a space SP is defined the upper surface 70U ofthe second porous part 70 and the lower surface 90L of the first porouspart 90. The space SP may be filled with at least one of the secondporous part 70 and the first porous part 90. That is the second porouspart 70 and the first porous part 90 may contact.

The second porous part 70 includes a ceramic porous body 71 includingmultiple pores and a ceramic insulating film 72. The ceramic porous body71 is provided to be tubular (for example, cylindrical) and is fitted tothe counter sunk portion 53 a. The shape of the second porous part 70 isdesired to be cylindrical, however is not limited to be cylindrical. Aninsulative material is used for the ceramic porous body 71. The materialof the ceramic porous body 71 is, for example, Al₂O₃, Y₂O₃, ZrO₂, MgO,SIC, AlN, Si₃N₄. The material of the ceramic porous body 71 may be glasssuch as SiO₂. The material of the ceramic porous body 71 may beAl₂O₃—TiO₂, SiO₂—MgO, Al₂O₃—SiO₂, Al₆O₁₃Si₂, YAG, ZrSiO₄ or the like.

A porosity of the ceramic porous body 71 is, for example, not less than20% and not more than 60%. A density of the ceramic porous body 71 is,for example, not less than 1.5 g/cm³ and not more than 3.0 g/cm³. Thegas such as He or the like which flows through the gas introduction path53 passes through the multiple pores of the ceramic porous body 71, andis sent to the groove 14 from the through hole 15 provided in theceramic dielectric substrate 11.

The ceramic insulating film 72 is provided between the ceramic porousbody 71 and the gas introduction path 53. The ceramic insulating film 72is denser than the ceramic porous body 71. A porosity of the ceramicinsulating film 72 is, for example, not more than 10%. A density of theceramic insulating film 72 is, for example, not less than 3.0 g/cm³ andnot more than 4.0 g/cm³. The ceramic insulating film 72 is provided o aside surface of the ceramic porous body 71.

A material of the ceramic insulating film 72 includes, for example,Al₂O₃, Y₂O₃, ZrO₂, MgO or the like. The material of the ceramicinsulating film 72 may include Al₂O₃—TiO₂, Al₂O₃—MgO, Al₂O3-SiO₂,Al₆O₁₃Si₂, YAG, ZrSiO₄ or the like.

The ceramic insulating film 72 is formed by thermal spraying on the sidesurface of the ceramic porous body 71. The thermal spraying is a methodthat a coating is formed by melting or softening a coating material byheating, accelerating in a particular form, making collide to the sidesurface of the ceramic porous body 71, and coagulating/depositing flatlycollapsed particles. The ceramic insulating film 72 may be manufacturedby, for example, PVD (Physical Vapor Deposition), CVD, sol-gel method,aerosol deposition method or the like. In the case of forming theceramic insulating film 72 by thermally spraying ceramic, a filmthickness is, for example, not less than 0.05 mm and not more than 0.5mm.

A porosity of the ceramic dielectric substrate 11 is, for example, notmore than 1%. A density of the ceramic dielectric substrate 11 is, forexample, 4.2 g/cm³.

The porosities of the ceramic dielectric substrate 11 and the secondporous part 70 are measured by a scanning electron microscopy asdescribed above. The density is measured on the basis of JIS C 21415.4.3.

If the second porous part 70 is fitted to the counter sunk portion 53 aof the gas introduction path 53, the ceramic insulating film 72 is in astate of contacting the base plate 50. That is, the ceramic porous body71 and the ceramic insulating film 72 which are highly insulative areintervened between the through hole 15 introducing the gas such as He orthe like to the groove 14 and the base plate made of a metal. Thissecond porous part 70 is used, and thus in comparison with the case ofproviding only the ceramic porous body 71 in the gas introduction path53, high insulating property can be demonstrated.

In the X-direction or the Y-direction, the dimension of the secondporous part 70 can be larger than the dimension of the first porous part90. Since a higher breakdown voltage is obtained by providing thissecond porous part 70, the arc discharge can be suppressed from beinggenerated more effectively.

The multiple pores provided in the second porous part 70 are dispersedmore three-dimensionally than the multiple pores provided in the firstporous part 90, and thus a ratio of pores piercing in the Z-directioncan be higher in the first porous part 90 than in the second porous part70. Since the higher breakdown voltage can be obtained by providing thesecond porous part 70 including the multiple pores dispersedthree-dimensionally, the arc discharge can be suppressed from beinggenerated more effectively. The gas flow can be facilitated by providingthe first porous part 90 having a large ratio of pores piercing in theZ-direction.

In the z-direction, the dimension of the second porous part 70 can belarger than the dimension of the first porous part 90. In this way, thehigher breakdown voltage can be obtained, and thus the arc discharge canbe suppressed from being generated more effectively.

An average value of the multiple pores provided in the second porouspart 70 can be larger than an average value of the multiple poresprovided in the first porous part 90. In this way, since the secondporous part 70 having a large pore diameter is provided, the gas flowcan be facilitated. Since the first porous part 90 having a small porediameter is provided on the suction object side, the arc discharge canbe suppressed from being generated more effectively.

Since the variation of the multiple pore diameters can be small, the arcdischarge can be suppressed from being generated more effectively.

FIG. 10 is a schematic cross sectional view illustrating the secondporous part of the electrostatic chuck according to the embodiment.

FIG. 10 is an enlarged view of a portion of the cross section of theceramic porous body 71.

Multiple pores 71 p provided in the ceramic porous body 71 are dispersedin the ceramic porous body 71 three-dimensionally in the X-direction,the Y-direction and the Z-direction. In other words, the ceramic porousbody 71 has a three dimensional network structure which broadens in theX-direction, the Y-direction and the Z-direction. The multiple pores 71p are dispersed in the ceramic porous body 71, for example, randomly.

Since the multiple pores are dispersed three-dimensionally, a portion ofthe multiple pores 71 p are exposed to a surface of the ceramic porousbody 71. For that reason, fine unevenness is formed on the surface ofthe ceramic porous body 71. That is, the surface of the ceramic porousbody 712 is rough. Since the surface of the ceramic porous body 71 isrough, the ceramic insulating film 72 which is a sprayed film can beeasily formed on the surface of the ceramic porous body 71. For example,the contact of the strayed film and the ceramic porous body 71 isimproved. The separation of the ceramic insulating film 72 can besuppressed.

The average value of the diameters of the multiple pores 71 p providedin the ceramic porous body 71 is larger than the average value of thediameters of the multiple pores 96 provided in the porous region 91. Thediameter of the pores 71 p is not less than 10 μm and not more than 50μm. The flow rate of the gas flowing through the through hole 15 can becontrolled (restricted) by the porous region 91 having a small porediameter. Thereby, the variation of the gas flow rate due to the ceramicporous body 71 can be suppressed. The measurement of the diameter of thepores 71 p and the diameter of the pores 96 can be performed by ascanning electron microscopy as described previously.

FIG. 11 is a schematic cross sectional view illustrating anotherelectrostatic chuck according to the embodiment.

FIG. 11 illustrates around the firs porous part 90 as well as FIG. 2A.

In this example, the hole part 15 b (the connecting hole connecting thefirst porous part 90 and the groove 14) is not provided in the throughhole 15 provided in the ceramic dielectric substrate 11. For example,the diameter (a length along the X-direction) of the through hole 15does not change in the Z-direction and is substantially constant.

As shown in FIG. 11, at least a portion of the upper surface 90U of thefirst porous part 90 is exposed to the first major surface 11 a side ofthe ceramic dielectric substrate 11. For example, a position in theZ-direction of the upper surface 90U of the first porous part 90 is thesame as a position in the Z-direction of a bottom or the groove 14.

In this way, the first porous part 90 may be disposed substantially overthe whole of the through hole 15. Since the connecting hole having asmall diameter cannot be provided in the through hole 15, the flow rateof the gas flowing through the through hole 15 can be large. The highlyinsulative first porous part 90 can be disposed in a most part of thethrough hole 15, and the high resistance to the arc discharge can beobtained.

FIG. 12 is a schematic cross sectional view illustrating anotherelectrostatic chuck according to the embodiment.

FIG. 12 illustrates around the firs porous part 90 as well as FIG. 2A.

In this example, the first porous part 90 is not integrated with theceramic dielectric substrate 11.

The adhesive member 61 (adhesive) is provided between the first porouspart 90 and the ceramic dielectric substrate 11. The first porous part90 is adhered to the ceramic dielectric substrate 11 by the adhesivemember 61. For example, the adhesive member 61 is provided between theside surface of the first porous part 90 (the side surface 93 s of thedense region 93) and the inner wall 15 w of the through hole 15. Thefirst porous part 90 and the ceramic dielectric substrate 11 may notcontact.

A silicone adhesive is used for the adhesive member 61, for example. Theadhesive member 61 is, for example, an elastic member having elasticity.Elasticity of the adhesive member 61 is, for example, lower thanelasticity of the dense region 93 of the first porous part 90, and lowerthan elasticity of the ceramic dielectric substrate 11.

In the structure where the first porous part 90 and the ceramicdielectric substrate 11 are adhered by the adhesive member 61, theadhesive member 61 can be a buffer material to a difference between heatshrinkage of the first porous part 90 and heat shrinkage of the ceramicdielectric substrate 11.

The embodiments of the invention have been described. However theinvention is not limited to the descriptions. For example, theconfiguration of the electrostatic chuck 110 based on Coulomb force hasbeen illustrated, however the configuration based on Johnson-Rahbeckforce is also applicable. Any design change of components, or anyaddition, omission in the above embodiments suitably made by thoseskilled in the art are also encompassed within the scope of theinvention as long as they fall within the spirit of the invention.Further, any components of the embodiments may be combined within theextent of technical feasibility and are included in the scope of theinvention to the extent that the feature of the invention is included.

What is claimed is:
 1. An electrostatic chuck, comprising: a ceramicdielectric substrate having a first major surface placing a suctionobject and a second major surface on an opposite side to the first majorsurface; a base plate supporting the ceramic dielectric substrate andincluding a gas introduction path; and a first porous part provided at aposition between the base plate and the first major surface of theceramic dielectric substrate and being opposite to the gas introductionpath, the first porous part including a plurality of sparse portionsincluding a plurality of pores and a dense portion having a densityhigher than a density of the sparse portions, each of the sparseportions extending in a first direction from the base plate toward theceramic dielectric substrate, the dense portion being positioned betweenthe plurality of sparse portions, the sparse portions including a wallportion provided between the pores and the pores, and a minimum value ofa dimension of the wall portion being smaller than a minimum value of adimension of the dense portion in a second direction substantiallyperpendicular to the first direction.
 2. The electrostatic chuckaccording to claim 1, wherein a dimension of the plurality of poresprovided in each of the plurality of sparse portions is smaller than thedimension of the dense portion in the second direction.
 3. Theelectrostatic chuck according to claim 1, wherein an aspect ratio of theplurality of pores provided in each of the plurality of sparse portionsis not less than
 30. 4. The electrostatic chuck according to claim 1,wherein a dimension of the plurality of pores provided in each of theplurality of sparse portions is not less than 1 micrometer and not morethan 20 micrometers in the second direction.
 5. The electrostatic chuckaccording to claim 1, wherein when viewed along the first direction, theplurality of pores includes a first pore positioned at a center portionof the sparse portions, and a number of pores of the plurality of poresadjacent to the first pore and surrounding the first pore is
 6. 6. Theelectrostatic chuck according to claim 1, further comprising: anelectrode provided between the first major surface and the second majorsurface, a distance in the second direction between the electrode and aporous region provided in the first porous part being longer than adistance in the first direction between the first major surface and theelectrode.
 7. The electrostatic chuck according to claim 1, furthercomprising: a second porous part provided between the first porous partand the gas introduction path, a dimension of the second porous partbeing larger than a dimension of the first porous part in the seconddirection.
 8. The electrostatic chuck according to claim 1, furthercomprising: a second porous part provided between the first porous partand the gas introduction path and including a plurality of pores, anaverage value of diameters of the plurality of pores provided in thesecond porous part being larger than an average value of diameters ofthe plurality of pores provided in the first porous part.
 9. Theelectrostatic chuck according to claim 1, further comprising: a secondporous part provided between the first porous part and the gasintroduction path and including a plurality of pores, fluctuation ofdiameters of the plurality of pores provided in the first porous partbeing smaller than fluctuation of diameters of the plurality of poresprovided in the second porous part.
 10. The electrostatic chuckaccording to claim 8, wherein a dimension of the second porous part islarger than a dimension of the first porous part in the first direction.11. The electrostatic chuck according to claim 8, wherein the pluralityof pores provided in the second porous part are more dispersed threedimensionally than the plurality of pores provided in the first porouspart, and a ratio of pores piercing in the first direction is larger inthe first porous part than the second porous part.
 12. The electrostaticchuck according to claim 1, wherein the first porous part and theceramic dielectric substrate include aluminum oxide as a main component,and a purity of the aluminum oxide of the ceramic dielectric substrateis higher than a purity of the aluminum oxide of the first porous part.13. The electrostatic chuck according to claim 9, wherein a dimension ofthe second porous part is larger than a dimension of the first porouspart in the first direction.
 14. The electrostatic chuck according toclaim 9, wherein the plurality of pores provided in the second porouspart is more dispersed three dimensionally than the plurality of poresprovided in the first porous part, and a ratio of pores piercing in thefirst direction is larger in the first porous part than the secondporous part.
 15. The electrostatic chuck according to claim 10, whereinthe plurality of pores provided in the second porous part is moredispersed three dimensionally than the plurality of pores provided inthe first porous part, and a ratio of pores piercing in the firstdirection is larger in the first porous part than the second porouspart.